This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-006947, filed Jan. 14, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an exposure apparatus for exposing a to-be-exposed object by using a photo mask.
In general, a color cathode-ray tube, for example, comprises a vacuum envelope with a panel having phosphor screen on its inner surface and a shadow mask that is opposed to the phosphor screen in the envelope. A large number of electron beam passage apertures are formed in the effective surface of the shadow mask. Electron beams emitted from an electron gun are applied to the phosphor screen through the electron beam passage apertures. The shadow mask, which is called a color selecting electrode, has a color selecting function such that the electron beams can be run against only those phosphor layers which are geometrically in one-to-one relation with the apertures.
Normally, a shadow mask is formed of a metallic sheet with a thickness of about 0.1 to 0.25 mm. such as aluminum-killed steel or low-thermal-expansion invar material (Fe-36% Ni), which is bored with tens of thousands to hundreds of thousands of infinitesimal circular or rectangular electron beam apertures. Each aperture is formed of a larger hole that opens in the screen-side surface of the shadow mask and a smaller hole that opens in the gun-side surface of the mask, the two holes communicating with each other.
Conventionally, the shadow mask of this type is manufactured by the photo-etching method using a first matrix corresponding to the larger holes and a second matrix corresponding to the smaller holes, as photo masks. The following is a description of the shadow mask manufacturing method.
After both surfaces of a thin metallic belt (shadow mask material), such as aluminum-killed steel or invar material, are first degreased and rinsed to remove rust resisting oil and soil thereon, a water-soluble resist, selected among resist materials based on casein-dichromates, PVA-dichromates, etc., is applied to the surfaces and dried.
After a pair of photo masks each having a given exposure pattern are then brought into vacuum contact with the opposite resist-coated surfaces of the thin metallic belt, individually, they are exposed through the photo masks. Subsequently, the exposed resist is developed, flushed, dried, and baked to form an etching pattern. In this state, the thin metallic belt is etched to form the electron beam passage apertures. Generally, the metallic belt is etched twice for its obverse and reverse sides if its apertures are circular which are mainly used in a shadow mask for displays. If the apertures are rectangular which are mainly used in a shadow mask for television sets, the metallic belt is etched at a time from both sides. Thereafter, the resist is separated. In the case where the metallic belt is etched twice for the opposite sides, the resist and a back coat that is applied after the reverse side is etched are separated, and finally, each shadow mask is cut off and completed.
In general, each photo mask used in an exposure process for a shadow mask is an emulsion mask that is obtained by applying an emulsion layer, which is formed of a gelatin film having a silver-nitrate-based sensitizer dispersed therein, to one surface of a green glass base, and forming on the emulsion layer a given exposure pattern that corresponds to apertures of the shadow mask.
In an exposure apparatus for shadow mask, the pair of photo masks formed in the aforethe manner are attached individually to vacuum-contact frames so that the exposure pattern surfaces or the emulsion layers face inward, and are opposed to each other with the thin metallic belt, having the resist formed on either surface thereof, between them. After the relative positions of the photo masks are aligned with high accuracy, the photo masks are brought individually into vacuum contact with the opposite surfaces of the metallic belt by means of the vacuum-contact frames. In this state, the resist is exposed through the photo masks by means of exposure means.
After exposure is finished, the vacuum contact is canceled so that the photo masks are separated from the thin metallic belt, and exposed portions of the belt are driven out of the vacuum-contact frames, whereupon one cycle of exposure operation terminates. Normally, a series of cycles of such operation is carried out continuously. In some cases, a large number of vacuum-contact frames and photo masks may be arranged so that a plurality of parts of the metallic belt can be exposed at a time.
However, the following problems will be aroused if resist layers on the opposite surfaces of the thin metallic belt are exposed to exposure patterns for the pair of photo masks by the aforethe method. Emulsion masks are low-priced and can be easily used as shadow masks or large-sized PDP masks. Since the gelatin film is used for the emulsion layers, however, the emulsion masks are low in film hardness and film strength and flaw easily. If foreign substances are sandwiched between these masks, therefore, they sink into the emulsion layers and become unremovable.
In the shadow mask exposure process, as described above, so-called hard-contact exposure is effected such that the resist layers and the emulsion layers are pressed hard against one another as the shadow mask is exposed. If foreign substances, such as slugs, dust, etc., are interposed between the resist layers and the emulsion layers, therefore, the emulsion layers, which are low in film hardness and film strength, may be marred, the exposure patterns may be partially broken off, or the foreign substances may remain sinking in the emulsion layers. This may result in formation of defective apertures in an exposure region, development of stains thereon, partial breakage of the exposure patterns, or formation of unnecessary opaque portions in the photo masks.
Once the emulsion masks are damaged in this manner, moreover, they can never recover afterward. If the damage is not noticed, therefore, all of shadow masks that are to be manufactured in the subsequent processes are subject to common failure in the same regions, so that the yield is lowered substantially. Once the thin metallic belt is etched, in particular, it can never recover any more, thus suffering great damage.
Shadow masks of color cathode-ray tubes that are used as displays of personal computers or various monitors, for example, require high-accuracy electron beam passage apertures with diameters of 0.10 to 0.15 mm, array pitches of 0.2 to 0.3 mm, and diameter accuracy within the range of xc2x13 xcexcm. If the emulsion masks suffer adhesion of foreign substances of sizes that arouse no problems in the manufacture of shadow masks of color cathode-ray tubes for ordinary TV sets, therefore, they are greatly influenced by the substances and rendered defective.
According to an exposure apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 8-124822, for example, a glass plate is opposed to a photo mask, and ionized gas is run into a space between them, whereby the photo mask is prevented from being charged and from collecting dust. However, this exposure apparatus is not provided with any measure to counter penetration or adhesion of foreign substances between the glass plate and a to-be-exposed object and between the photo mask and the object. Accordingly, this apparatus is not adapted for the aforethe hard-contact exposure.
The present invention has been contrived in consideration of these circumstances, and its object is to provide an exposure apparatus capable of preventing penetration of foreign substances between a to-be-exposed object and photo masks so that the incidence of failure that is attributable to damage to the photo masks can be lowered to facilitate high-yield exposure.
In order to achieve the above object, an exposure apparatus according to the present invention comprises a mask support portion opposed to a to-be-exposed object, supporting a photo mask having an exposure pattern thereon, and configured to move the photo mask between an exposure position in which the photo mask is in contact with the to-be-exposed object and a separate position in which the photo mask is kept off the object; an exposure light source arranged to expose the to-be-exposed object through the photo mask in the exposure position; and a clean air supplier configured to run clean air between the to-be-exposed object and the photo mask when the photo mask is moved to the separate position.
According to this exposure apparatus, the clean air is supplied from the clean air supplier at least to the region between the to-be-exposed object and the photo mask in the separate position. By doing this, foreign substances can be prevented from adhering to the to-be-exposed object or the photo mask during an exposure process, and foreign substances that adhere to the object can be removed. Thus, foreign substances can be prevented from penetrating or jamming into the region between the to-be-exposed object and the photo mask, and the incidence of failure that is attributable to damage to the photo mask can be lowered.
Further, the clean air supplier includes a first supply portion configured to supply the clean air to the region between the to-be-exposed object and the photo mask when the photo mask is moved to the separate position and a second supply portion configured to supply the clean air to the outer surface of the photo mask when the photo mask is moved to the separate position and when the photo mask is moved to the exposure position. When the to-be-exposed object and the photo mask are in contact with each other, the clean air is supplied from the second supply portion only. When the object and the photo mask are separate, the clean air is supplied from both the first and second supply portions. The first supply portion serves to adjust the supply of the clean air depending on the movement of the photo mask.
As described above, the clean air from the second supply portion is supplied along the outer surface of the photo mask when the to-be-exposed object and the photo mask is in contact with each other, that is, during exposure. By doing this, the photo mask that is heated by heat rays from the exposure light source during exposure can be cooled, so that dislocation that is attributable to thermal expansion of the photo mask can be reduced to facilitate high-accuracy exposure. In this case, a satisfactory cooling effect can be obtained if the wind speed of the clean air that flows over the outer surface of the photo mask that is in contact with the to-be-exposed object is at 4.7 m/sec or more. Further, a satisfactory dust removing effect can be obtained if the wind speed of the clean air that flows between the to-be-exposed object and the photo mask that are separate from each other is at 2.7 m/sec or more.
Foreign substances can be prevented from adhering to the to-be-exposed object or the photo mask during the exposure process by ionizing the clean air alternately for positive and negative charges by means of ionization means.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.